Phytoplankton Groups Research Articles

Detection and Quantification of Small Noncoding RNAs in Marine Diatoms.

Endogenous small noncoding RNAs (sRNAs) are a large family of essential regulators of gene expression in both eukaryotes and prokaryotes. Various types of sRNAs with different size and mapping to different genome locations have been recently identified in diatoms, a successful group of phytoplankton in the marine environment. However, their biogenesis and regulatory function are still largely unknown and unexplored in these microalgae, also due to the lack of methods for their experimental analysis. Herein, we present a point-by-point description of the protocols for detection and quantification of sRNAs by Northern-blot analysis and quantitative stem-loop RT-PCR, established in the diatom molecular model specie Phaeodactylum tricornutum.

In contrast to diatoms, cryptophytes are susceptible to iron limitation, but not to ocean acidification.

Previous field studies in the Southern Ocean (SO) indicated an increased occurrence and dominance of cryptophytes over diatoms due to climate change. To gain a better mechanistic understanding of how the two ecologically important SO phytoplankton groups cope with ocean acidification (OA) and iron (Fe) availability, we chose two common representatives of Antarctic waters, the cryptophyte Geminigera cryophila and the diatom Pseudo-nitzschia subcurvata. Both species were grown at 2°C under different pCO2 (400 vs. 900 μatm) and Fe (0.6 vs. 1.2 nM) conditions. For P. subcurvata, an additional high pCO2 level was applied (1400 μatm). At ambient pCO2 under low Fe supply, growth of G. cryophila almost stopped while it remained unaffected in P. subcurvata. Under high Fe conditions, OA was not beneficial for P. subcurvata, but stimulated growth and carbon production of G. cryophila. Under low Fe supply, P. subcurvata coped much better with OA than the cryptophyte, but invested more energy into photoacclimation. Our study reveals that Fe limitation was detrimental for the growth of G. cryophila and suppressed the positive OA effect. The diatom was efficient in coping with low Fe, but was stressed by OA while both factors together strongly impacted its growth. The distinct physiological response of both species to OA and Fe limitation explains their occurrence in the field. Based on our results, Fe availability is an important modulator of OA effects on SO phytoplankton, with different implications on the occurrence of cryptophytes and diatoms in the future.

Food spectrum dynamics of anadromous Hilsa, Tenualosa ilisha (Hamilton, 1822) inhabiting River Brahmaputra, India curtailing apprehension of food selectivity: An insight into its domestication

Food and feeding habits of Tenualosa ilisha collected from two sampling locations in Brahmaputra River, Assam, India for a period of 12 months from May 2018 to April 2019 were studied. Index of preponderance revealed semi-digested animal matter (25.92 %) as the most dominant food item followed by Bacillariophyta (23.32 %). 31 genera of phytoplankton and 15 genera of zooplankton were observed in the gut of the species. Major groups of zooplankton include cladocerans, copepods, followed by rotifers, while diatoms, green algae and blue green algae were dominant phytoplankton groups. The anadromous tropical shad is planktivorous by nature and has a preference for zooplankton in smaller size groups (< 250 mm) and phytoplankton in larger size groups (> 250 mm). GaSI values (mean±SE) ranged from 1.50±0.14 to 6.93±0.89 and HSI values from 0.58±0.06 to 1.54±0.15. Index of fullness was found to range from 7.08±0.42 to 1.81±0.40. Feeding intensity, GaSI, HSI values showed seasonal variation, found to be low during October to December and high during February to June. Size group-wise analysis of feeding intensity showed high feeding intensity in lower size groups (< 250 mm) and comparatively low feeding intensity and high percentage of empty stomachs in higher size groups (> 250 mm). RLG values ranged from 1.181±0.028 to 1.450±0.052. Monthly average RLG values were found to be highest during November and in the size group of 351 – 400 mm. Changes in food composition were noticed in both months and as well as size groups.

Proteomic analysis of metabolic pathways supports chloroplast-mitochondria cross-talk in a Cu-limited diatom.

Diatoms are one of the most successful phytoplankton groups in our oceans, being responsible for over 20% of the Earth's photosynthetic productivity. Their chimeric genomes have genes derived from red algae, green algae, bacteria, and heterotrophs, resulting in multiple isoenzymes targeted to different cellular compartments with the potential for differential regulation under nutrient limitation. The resulting interactions between metabolic pathways are not yet fully understood. We previously showed how acclimation to Cu limitation enhanced susceptibility to overreduction of the photosynthetic electron transport chain and its reorganization to favor photoprotection over light harvesting in the oceanic diatom Thalassiosira oceanica (Hippmann et al., 2017, 10.1371/journal.pone.0181753). In order to gain a better understanding of the overall metabolic changes that help alleviate the stress of Cu limitation, we have further analyzed the comprehensive proteomic datasets generated in that study to identify differentially expressed proteins involved in carbon, nitrogen, and oxidative stress‐related metabolic pathways. Metabolic pathway analysis showed integrated responses to Cu limitation. The upregulation of ferredoxin (Fdx) was correlated with upregulation of plastidial Fdx‐dependent isoenzymes involved in nitrogen assimilation as well as enzymes involved in glutathione synthesis, thus suggesting an integration of nitrogen uptake and metabolism with photosynthesis and oxidative stress resistance. The differential expression of glycolytic isoenzymes located in the chloroplast and mitochondria may enable them to channel both excess electrons and/or ATP between these compartments. An additional support for chloroplast–mitochondrial cross‐talk is the increased expression of chloroplast and mitochondrial proteins involved in the proposed malate shunt under Cu limitation.

Amino acid nitrogen stable isotopes as biomarkers of coastal phytoplankton assemblages and food web interactions

Marine phytoplankton and zooplankton face rapidly changing environments in the face of global warming and climate change. We investigated the effect of warmer water and lower pH conditions—projected for New Zealand coastal waters at the start of the next century—on both phytoplankton and zooplankton in a 20 d mesocosm experiment to determine whether amino acid stable isotopes could be used as biomarkers of environmental change. We also assessed whether key environmental drivers, such as those linked to climate change, altered the processing of amino acids at the base of the food web. Despite changes in phytoplankton biomass and community composition, we found no significant difference in either particulate organic matter (POM) bulk or amino acid-specific δ15N values, indicating that the trophic status of POM was not significantly influenced by lower pH and warming. Threonine δ15N values were the most sensitive to changes in the phytoplankton community and showed correlations with diatoms (positive) and small flagellates (negative), demonstrating potential as a biomarker for detecting changes related to these phytoplankton groups and thus making threonine a promising indirect indicator of climate change. Finally, δ15NPhe values tracked changes in the lower food web, likely due to faster turnover times, showing its valuable role as a tracer of the nitrogen baseline, even during accelerated metabolism in zooplankton.

Qualidade da água e comunidade planctônica do reservatório Owalla, Estado de Osun, sudoeste da Nigéria

Abstract Aim Owalla Reservoir, one of the largest and oldest man-made lakes in Osun State supplies potable water to many towns in the state including the state capital, Osogbo. Active fishing activities also takes place in the lake. Inspite of the importance of the reservoir, information on the planktonic community and physico-chemical water quality are scarce. Therefore, this study investigated the water quality and plankton composition of Owalla Reservoir, Osun State, Nigeria, from October 2012 to November 2013 with a view to providing baseline information on limnology of the reservoir. Methods Seven sampling stations (designated Stations 1-7) were established as representatives of the zones and regions of the reservoir and sampling was conducted quarterly. At Stations 1 and 3, only surface water samples were collected while water samples were collected from the surface, mid-depth and close to the bottom at other stations. Samples for total plankton and physico-chemical water quality were analyzed using standard methods. Results The result of the study showed that mean dissolved oxygen (P&lt;0.001), biochemical oxygen demand, conductivity, pH (P&lt;0.001), and alkalinity were higher at the surface of the reservoir. As regards seasonal variation, alkalinity, biochemical oxygen demand had the higher mean values during the rainy season. Also, acidity, dissolved oxygen, and pH showed significantly (P&lt;0.001) higher values during the rainy season. One hundred and thirty-seven (137) taxa of phytoplankton and 39 taxa of zooplankton were recorded from the reservoir. The horizontal pattern of variation showed an increase in the mean abundance of most of phytoplankton groups from inflow to the dam area while vertical variation showed a decrease in mean abundance from surface to the bottom of the reservoir. Most of the phytoplankton and zooplankton taxa were more abundant during the dry season than in the rainy season. Conclusions The study concluded that all the monitored physico-chemical water quality parameters were within the guide level range as of the World Health Organisation (WHO) for drinking water, Owalla Reservoir is qualitatively rich in both phytoplankton and zooplankton and the reservoir can support a viable aquatic community and sustainable fishery production.

Phytoplankton community structure changes in Thi Nai lagoon (South - Central Vietnam) from 2004 to 2020

Phytoplankton species composition, abundance, biodiversity indices and their influence by environmental conditions were examined in Thi Nai lagoon using data from four surveys in 2004, 2008, 2009 and 2020. A total of 367 taxa of phytoplankton belonging to ten groups was recorded, of which diatoms were dominant with over 60% of the total species. In Thi Nai lagoon, the number of phytoplankton species decreased from the upper lagoon (283 taxa) to the lagoon mouth area (224) and was lowest in river stations (139). The species number was much lower in the rainy season (&lt;95 species) and increased from 2004 to 2020. Among the biodiversity indices, Shannon, ∆, s∆+, Λ+ and sФ+ were lower in the rainy season, whereas ∆*, ∆+ and Ф+ had lower values in the dry season. For long-term analysis, the differences were especially significant at upper and lower lagoon for ∆, ∆*, ∆+, s∆+ and sФ+. In the dry season, the mean density of phytoplankton was lower at the river stations and upper lagoon, but higher at the lower lagoon and the lagoon mouth area. There was a clear difference of species assemblages between the two seasons with average dissimilarities in each area ranging from 94.16% to 95.57%. During 2004–2020, the difference in ratios between the main phytoplankton groups were small over years but there was a complete change in dominance of particular species, assemblage dissimilarities were from 73.4 to 77.9, greatest between 2009 and 2020. The lagoon was low in biodiversity for the whole investigated time indicated by taxonomic index ∆+. Among biodiversity indices, species richness (S), taxonomic indices (∆*, s∆+), and phylogenetic indices (Ф+, sФ+) were more sensitive to the changes of the aquatic environment than other traditional indices.

Dynamics of phytoplankton groups in three contrasting situations of the open NW Mediterranean Sea revealed by pigment, microscopy, and flow cytometry analyses

A detailed study of phytoplankton composition and dynamics was carried out during three contrasting situations (cruises F1, F2, and F3) in the northwestern (NW) Mediterranean Sea. Haptophytes, diatoms, and green algae dominated in F1, during the spring bloom, with high nutrients and high phytoplankton biomass. In F2, the post-bloom situation with a still weak stratification and lower nutrient concentrations, we found a high spatial variability. Stations were clearly dominated by either Synechococcus, haptophytes or cryptophytes; with Synechococcus reaching the highest abundance (4 × 105 cells mL−1, 60% of the integrated chlorophyll a) reported to date for the open Mediterranean Sea. Cryptophytes accumulated close to the surface in very shallow mixed layer stations. In late summer, F3 revealed a fully developed stratification with low nutrients and a marked deep chlorophyll maximum (DCM). Prochlorococcus was present only during this cruise, mainly in deep layers together with haptophytes and pelagophytes, while haptophytes and Synechococcus dominated the upper mixed layer. Flow cytometry (FCM) and pigment-based abundance estimates for Prochlorococcus, Synechococcus and cryptophytes were well correlated, as happened also between small picoeukaryotes (FCM) and green algae (pigments), and between large picoeukaryotes (FCM) and haptophytes (pigments). Dinoflagellate abundance by microscopy and by pigments did not agree well, probably due to the presence of heterotrophic forms or because they contained pigments other than peridinin, the standard dinoflagellate marker. The decrease in size of the FCM large picoeukaryotes group with depth was presumably related to the increasing contribution of pelagophytes, with smaller cells than haptophytes, the other main component of this fraction. Cell size increase of Prochlorococcus and Synechococcus with depth suggests vertical segregation of genotypes or photoadaptation. The groups' ecological preferences are presented with respect to depth and nutrient concentrations. Synechococcus and cryptophytes occupied shallow layers; diatoms, green algae and Prochlorococcus showed a tendency for deep layers and pelagophytes for even deeper layers, while haptophyte and dinoflagellate allocations were less clear. As for nutrients, the maximum relative contributions of green algae and especially diatoms occurred when dissolved inorganic phosphorus (DIP) concentrations were highest, of Prochlorococcus, dinoflagellates and pelagophytes when lowest, and of Synechococcus and cryptophytes when DIP concentrations were low but not minimal. The contribution of haptophytes did not show a relationship with DIP concentration. These results from individual groups stand as significant exceptions to the general relationship between phytoplankton cell size and nutrient availability.

Do Cross-Latitude and Local Studies Give Similar Predictions of Phytoplankton Responses to Warming? An Analysis of Monitoring Data from 504 Danish Lakes

Cross-latitude studies on lakes have a potential to predict how global warming may cause major changes in phytoplankton biomass and composition, e.g., the development of favourable conditions for cyanobacteria dominance. However, results from these studies may be influenced by biogeographical factors, and the conclusions may, therefore, not hold when considering local response patterns. We used monthly monitoring data from 504 lakes in Denmark—a small and homogeneous geographical region—to establish empirical relationships between key phytoplankton groups and a set of explanatory variables including total phosphorus (TP), total nitrogen (TN), lake mean depth (DEP) and water temperature (TEMP). All variables had strong effects on phytoplankton biomass and composition, but their contributions varied over the seasons, with TEMP being particularly important in June–October. We found dominance of cyanobacteria in terms of biomass and also an increase in dinophytes biomass at higher TEMP, while diatoms and chlorophytes became less important. In May, however, the TEMP effect on total phytoplankton biomass was negative, likely reflecting intensified zooplankton grazing. Our results suggest that biogeographical effects are of minor importance for the response patterns of phytoplankton to temperature and that substantial concentration reductions of TN and TP are needed in eutrophic lakes to counteract the effect of the climate change-induced increase in TEMP.

Cyclic evolution of phytoplankton forced by changes in tropical seasonality.

Although the role of Earth's orbital variations in driving global climate cycles has long been recognized, their effect on evolution is hitherto unknown. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable a detailed assessment of the effect of cyclic orbital-scale climate changes on evolution because of their abundance in marine sediments and the preservation of their morphological adaptation to the changing environment1,2. Evolutionary genetic analyses have linked broad changes in Pleistocene fossil coccolith morphology to species radiation events3. Here, using high-resolution coccolith data, we show that during the last 2.8 million years the morphological evolution of coccolithophores was forced by Earth's orbital eccentricity with rhythms of around 100,000 years and 405,000 years-a distinct spectral signature to that of coeval global climate cycles4. Simulations with an Earth System Model5 coupled with an ocean biogeochemical model6 show a strong eccentricity modulation of the seasonal cycle, which we suggest directly affects the diversity of ecological niches that occur over the annual cycle in the tropical ocean. Reduced seasonality in surface ocean conditions favours species with mid-size coccoliths, increasing coccolith carbonate export and burial; whereas enhanced seasonality favours a larger range of coccolith sizes and reduced carbonate export. We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year cyclicity that is seen in global carbon cycle records.

Microplanktonic diatom assemblages dominated the primary production but not the biomass in an Antarctic fjord

The western Antarctic Peninsula (WAP) fjords, currently threatened by climate change, are known as high krill congregation areas, however, the primary productivity in relation to phytoplankton groups in these coastal areas remains uncertain. To test this, we studied the specific composition, diversity and cellular carbon content of phytoplankton communities in relation to primary production (PP) and growth rates in Andvord Bay, its connection to Gerlache Strait and a near station on the continental shelf during spring (2015) and autumn (2016). Based on the microscopic determination of the relative biomass of the different microalgal taxa we determined three main phytoplankton assemblages that differ in their composition, PP, growth, and spatial and temporal distribution: (1) an assemblage dominated by cryptophytes, with high biomass (59.2 ± 28.2 μgC L−1), intermediate PP (63.1 ± 32 mgC m−3 d−1), and low growth (0.2 ± 1.1 d−1) present in the inner part of the fjord during spring, and related to higher surface water temperatures; (2) an assemblage dominated by microplanktonic diatoms (mainly Odontella weissflogii) with intermediate biomass (40.1 ± 17.2 μgC L−1), high PP (151.2 ± 62.5 mgC m−3 d−1), and high growth (0.9 ± 1 d−1) present from the fjord mouth to the Gerlache Strait waters during spring and in shelf waters during autumn, related to high irradiance and microzooplankton biomass; and (3) an assemblage dominated by dinoflagellates, mainly small gymnodinioids (< 15 μm long), with low biomass (3.5 ± 3.5 μgC L−1), low PP (6.9 ± 5.1 mgC m−3 d−1), and intermediate growth (0.5 ± 0.6 d−1) present in the whole fjord and the Gerlache Strait during autumn and infrequently during spring, related to high meltwater fraction. During both seasons, the highest phytoplankton biomass, richness and productivity in Andvord Bay was located in a frontal area at the fjord's mouth. Overall, the results of this study support the notion that WAP fjords are highly productive, highlighting the role of microplanktonic diatom as the main organic carbon producers, even when they occur in low abundances, due to their photosynthetic potential and higher Carbon-to-Chlorophyll a ratio. Our results, together with previous phytoplankton growth rates measured in the WAP nearshore waters from King George Island to Marguerite Bay, are higher than those measured on the WAP shelf and in the Ross Sea suggesting micro- and macronutrient enrichment from glacial melt maintains high productivity throughout the growth season in fjords. Our results support the hypothesis that climate change could highly affect the coastal WAP ecosystems by changing the balance between more productive phytoplankton assemblages (diatoms) to considerably less productive phytoplankton assemblages (cryptophytes).

Diagnosis of ecological quality of Dohou Lake on the basis of environmental parameters and phytoplankton community, Western Côte d’Ivoire

The ecological quality of Dohou Lake in Duékoué was determined from the phytoplankton community and physico-chemical parameters. All of the stations in Dohou Lake are dominated by Cyanobacteria and Bacillariophyta individuals, with high monthly proportions observed during the study period. Ecological indicators such as total phosphorus, transparency and chlorophyll made it possible to assess the physico-chemical quality of the environment. Thus, mean total phosphorus values ranged from 970 to 1150 µg/L from station D7 to station D6. Minimum transparency values ranged from 0.1 to 0.5 m from station D7 to D3, and mean values ranged from 0.3 m (station D7) to 0.69 m (station D1). For chlorophyll a, mean values ranged from 3.52 µg/L to 12.98 µg/L from station D7 to station D2, with maximum values for this parameter ranging from 13.4 µg/L (station D7) to 46.73 µg/L (station D2). All of the stations on Dohou lake are therefore in an eutrophic state. The monthly variations in the different proportions of phytoplankton groups observed indicate a clear predominance of Cyanobacteria followed by Bacillariophyta. The values of the Planktonic Index (PI) indicate that the stations are in average ecological condition, except for station D7, which is in poor ecological condition. These ecological qualities are reflected by the spatial and temporal dominance of 4 functional groups which are C, LM, K, and S1.

Gut Content Analysis of Labeo Calbasu at Different Seasons in Dekhar Haor, Sunamgonj, Bangladesh

This research was conducted to find out the seasonal (monsoon and post monsoon) variation in gut contents of Labeo calbasu from June to November, 2016 in Dekhar haor of Sunamgonj district, Bangladesh. Three orders of phytoplankton were identified from the gut content viz. Bacillariophyceae (11 genera), Chlorophyceae (9 genera), and Cyanophyceae (4 genera). Bacillariophyceae (6.98±1.61×103cell/L) were identified as the most dominant phytoplankton group. Two types of zooplankton viz. crustacean (5 genera) and rotifer (5 genera) were identified. Crustaceans (0.88±0.4×103cell/L) were identified as the dominant group among zooplankton. Feeding intensity (average index of fullness, Gastrosomatic index) was higher in the post monsoon season compared with the monsoon season. The findings concluded that L. calbasu prefers phytoplankton over zooplankton, and the plankton consumption was slightly higher in the post-monsoon season than in the monsoon season. This research is expected to be crucial in the management and conservation of endangered L. calbasu in open waters, as well as provide baseline work for future research and open the path for captive aquaculture.

Microbial communities associated with sinking particles across an environmental gradient from coastal upwelling to the oligotrophic ocean

Complex interactions between microbial communities in the epipelagic and mesopelagic ocean drive variability in sinking carbon flux as part of the biological carbon pump. To investigate the relative contribution of dominant prokaryotic, protistan, and phytoplankton taxa to sinking particles, we used 16S/18S rRNA gene sequencing of particles collected in sediment traps and water column communities. Comparisons were done across a coastal upwelling-to-oligotrophic environmental gradient in the southern California Current Ecosystem to assess effects of natural environmental variability on taxon-specific contributions to sinking particle export. Particle-associated microbial assemblages differ from ambient mixed-layer communities. Gammaproteobacteria, dinoflagellates, and rhizarians were dominant microbes associated with sinking particles at all sampling locations, with diatoms increasing significantly at the inshore mesotrophic site. Parasitic groups, syndiniales and apicomplexans, were also major particle-associated taxa. Relative sequence abundance on exported particles from the mesotrophic inshore site more closely resembled the water-column dominants (especially diatoms) found above, while oligotrophic communities exhibited greater dissimilarity between the microbial communities on sinking particles and in the mixed layer. Protists generally showed greater similarity between mixed-layer and sinking particle communities than prokaryotes. Synechococcus was over-represented on sinking particles (relative to eukaryotic phytoplankton and other cyanobacteria) only in oligotrophic areas. Diatoms were the only phytoplankton group consistently over-represented on sinking particles across the region. Our results highlight important variability in microbial contributions to export that seem to align with differences in dominant grazing pathways. At the upwelling influenced site where export was primarily due to the fecal pellets of large copepods, diatoms were dominant contributors to export and protistan communities on sinking particles resembled those in the water column above. When doliolids were abundant, dinoflagellates contributed substantially to export, while the dominant picoeukaryote (Ostreococcus) was only a minor contributor. In oligotrophic areas, where grazing pathways were dominated by protists and sinking particles were primarily amorphous aged aggregates, there was little similarity between mixed layer and sinking particle communities.

Composition and Dominance of Edible and Inedible Phytoplankton Predict Responses of Baltic Sea Summer Communities to Elevated Temperature and CO2.

Previous studies with Baltic Sea phytoplankton combining elevated seawater temperature with CO2 revealed the importance of size trait-based analyses, in particular dividing the plankton into edible (>5 and <100 µm) and inedible (<5 and >100 µm) size classes for mesozoopankton grazers. While the edible phytoplankton responded predominantly negative to warming and the inedible group stayed unaffected or increased, independent from edibility most phytoplankton groups gained from CO2. Because the ratio between edible and inedible taxa changes profoundly over seasons, we investigated if community responses can be predicted according to the prevailing composition of edible and inedible groups. We experimentally explored the combined effects of elevated temperatures and CO2 concentrations on a late-summer Baltic Sea community. Total phytoplankton significantly increased in response to elevated CO2 in particular in combination with temperature, driven by a significant gain of the inedible <5 µm fraction and large filamentous cyanobacteria. Large flagellates disappeared. The edible group was low as usual in summer and decreased with both factors due to enhanced copepod grazing and overall decline of small flagellates. Our results emphasize that the responses of summer communities are complex, but can be predicted by the composition and dominance of size classes and groups.

Temporal Stability of Phytoplankton Functional Groups Within Two Agricultural Irrigation Ponds in Maryland, USA

Phytoplankton functional groups and their influence on water quality have been studied in various types of water bodies but have yet to be studied in agricultural irrigation ponds. Freshwater sources (e.g., lakes, rivers, and reservoirs) have been previously shown to exhibit high spatial and temporal variability in phytoplankton populations. Improvements in the monitoring of phytoplankton populations may be achieved if patterns of stable spatial variability can be found in the phytoplankton populations through time. The objective of this work was to determine if temporally stable spatial patterns in phytoplankton communities could be detected in agricultural irrigation ponds using a functional group approach. The study was performed at two working agricultural irrigation ponds located in Maryland, USA over two summer sampling campaigns in 2017 and 2018. Concentrations of four phytoplankton groups, along with sensor-based and fluorometer based water quality parameters were measured. Temporal stability was assessed using mean relative differences between measurements in each location and averaged measurements across ponds on each sampling date. Temporally stable spatial patterns of three phytoplankton functional groups were found for both ponds over the two sampling seasons. Both ponds had locations where specific phytoplankton functional group concentrations were consistently higher or lower than the pond's average concentration for each sampling date. Zones of consistently higher or lower than average concentrations were associated with flow conditions, pond morphology, and human activities. The existence of temporally stable patterns of phytoplankton functional group concentrations can affect the outcome of a water quality assessment and should be considered in water quality monitoring designs.

An 18S V4 rRNA metabarcoding dataset of protist diversity in the Atlantic inflow to the Arctic Ocean, through the year and down to 1000 m depth

Abstract. Arctic marine protist communities have been understudied due to challenging sampling conditions, in particular during winter and in deep waters. The aim of this study was to improve our knowledge on Arctic protist diversity through the year, in both the epipelagic (&lt; 200 m depth) and mesopelagic zones (200–1000 m depth). Sampling campaigns were performed in 2014, during five different months, to capture the various phases of the Arctic primary production: January (winter), March (pre-bloom), May (spring bloom), August (post-bloom), and November (early winter). The cruises were undertaken west and north of the Svalbard archipelago, where warmer Atlantic waters from the West Spitsbergen Current meet cold Arctic waters from the Arctic Ocean. From each cruise, station, and depth, 50 L of seawater was collected, and the plankton was size-fractionated by serial filtration into four size fractions between 0.45–200 µm, representing picoplankton (0.45–3 µm), small and large nanoplankton (3–10 and 10–50 µm, respectively), and microplankton (50–200 µm). In addition, vertical net hauls were taken from 50 m depth to the surface at selected stations. The net hauls were fractionated into the large nanoplankton (10–50 µm) and microplankton (50–200 µm) fractions. From the plankton samples DNA was extracted, the V4 region of the 18S rRNA-gene was amplified by polymerase chain reaction (PCR) with universal eukaryote primers, and the amplicons were sequenced by Illumina high-throughput sequencing. Sequences were clustered into amplicon sequence variants (ASVs), representing protist genotypes, with the dada2 pipeline. Taxonomic classification was made against the curated Protist Ribosomal Reference database (PR2). Altogether, 6536 protist ASVs were obtained (including 54 fungal ASVs). Both ASV richness and taxonomic composition varied between size fractions, seasons, and depths. ASV richness was generally higher in the smaller fractions and higher in winter and the mesopelagic samples than in samples from the well-lit epipelagic zone during summer. During spring and summer, the phytoplankton groups diatoms, chlorophytes, and haptophytes dominated in terms of relative read abundance in the epipelagic zone. Parasitic and heterotrophic groups such as Syndiniales and certain dinoflagellates dominated in the mesopelagic zone all year, as well as in the epipelagic zone during the winter. The dataset is available at https://doi.org/10.17882/79823 (Egge et al., 2014).

Feeding Ecology of Three Euphausiid Species in the North Pacific Ocean Inferred From 18S V9 Metabarcoding and Stable Isotope Analysis

Euphausiids are abundant micronekton and important links between higher and lower trophic levels in marine ecosystems; however, their detailed diets cannot be fully understood by conventional microscopy, especially in subtropical areas. Here, we report the euphausiid community structure in the California Current (CC) area and the eastern/western North Pacific subtropical gyre (ESG and WSG) and detail the feeding ecology of the dominant species (Euphausia pacifica, E. brevis, and E. hemigibba) in each region using a combined approach of gut content analysis via 18S V9 metabarcoding and stable carbon and nitrogen isotope analysis. A pronounced omnivorous feeding of all studied euphausiid species was supported by both methods: phytoplanktonic taxonomic groups (Dinophyta, Stramenopiles, and Archaeplastida), Copepoda, and Hydrozoa were detected in the gut contents; all the three euphausiid species displayed an intermediate trophic position between the net plankton (0.2–1.0 mm) and the myctophid fish (15.2–85.5 mm). However, Hydrozoa found in euphausiid gut contents likely derived from a potential cod-end feeding, based on isotope analysis. E. pacifica in the CC province ingested more autotrophic prey, including pelagophyte and green algae, due to a greater abundance of Stramenopiles and Archaeplastida in shallow layers of CC water. On the other hand, non-autotrophic prey such as mixotrophic Kareniaceae dinoflagellates, Pontellidae and Clausocalanidae copepods, and Sphaerozoidae rhizarian contributed more to the diets of E. brevis and E. hemigibba because of a lower chlorophyll a concentration or potentially a scarcity of autotrophic prey availability in ESG and WSG. The feeding patterns of dominant euphausiid species conducting filter feeding were thus largely determined by phytoplankton prey availability in the environments. Dietary difference across three species was also indicated by stable isotope analysis, with a lower mean trophic level of E. pacifica (2.32) than E. brevis (2.48) and E. hemigibba (2.57). These results verify direct trophic interactions between euphausiids and primary production and suggest that the omnivorous feeding habit is a favorable character for dominant Euphausia species.

Disentangling the Effects of Ocean Carbonation and Acidification on Elemental Contents and Macromolecules of the Coccolithophore Emiliania huxleyi.

Elemental contents change with shifts in macromolecular composition of marine phytoplankton. Recent studies focus on the responses of elemental contents of coccolithophores, a major calcifying phytoplankton group, to changing carbonate chemistry, caused by the dissolution of anthropogenically derived CO2 into the surface ocean. However, the effects of changing carbonate chemistry on biomacromolecules, such as protein and carbohydrate of coccolithophores, are less documented. Here, we disentangled the effects of elevated dissolved inorganic carbon (DIC) concentration (900 to 4,930μmolkg−1) and reduced pH value (8.04 to 7.70) on physiological rates, elemental contents, and macromolecules of the coccolithophore Emiliania huxleyi. Compared to present DIC concentration and pH value, combinations of high DIC concentration and low pH value (ocean acidification) significantly increased pigments content, particulate organic carbon (POC), and carbohydrate content and had less impact on growth rate, maximal relative electron transport rate (rETRmax), particulate organic nitrogen (PON), and protein content. In high pH treatments, elevated DIC concentration significantly increased growth rate, pigments content, rETRmax, POC, particulate inorganic carbon (PIC), protein, and carbohydrate contents. In low pH treatments, the extents of the increase in growth rate, pigments and carbohydrate content were reduced. Compared to high pH value, under low DIC concentration, low pH value significantly increased POC and PON contents and showed less impact on protein and carbohydrate contents; however, under high DIC concentration, low pH value significantly reduced POC, PON, protein, and carbohydrate contents. These results showed that reduced pH counteracted the positive effects of elevated DIC concentration on growth rate, rETRmax, POC, PON, carbohydrate, and protein contents. Elevated DIC concentration and reduced pH acted synergistically to increase the contribution of carbohydrate–carbon to POC, and antagonistically to affect the contribution of protein–nitrogen to PON, which further shifted the carbon/nitrogen ratio of E. huxleyi.

Diverse but uncertain responses of picophytoplankton lineages to future climate change

AbstractClimate change is projected to modify the physical and chemical environment of the ocean, but the quantitative impact on the distribution of phytoplankton groups is unclear. Most Earth System Models (ESMs) predict future declines of phytoplankton in low latitude waters, contradicting observations showing that picophytoplankton can reach high abundance in warm waters. Here, we used a historic and three climate scenarios along with quantitative niche models to project Prochlorococcus, Synechococcus, and picoeukaryotic phytoplankton distributions for the year 2100. First, we found global responses with up to 50% and 9% increase for Prochlorococcus and Synechococcus abundances, respectively, and 8% decrease for picoeukaryotic phytoplankton. All groups increased in abundance at low latitude, and Synechococcus and picoeukaryotic phytoplankton showed bands of decreases and increases in mid‐ and high‐latitudes, respectively. Prochlorococcus temporal trends were consistent among ESMs and increased with the strength of the scenario, while Synechococcus and picoeukaryotic phytoplankton showed mixed results. Second, we evaluated sources of uncertainty associated to future projections. The anthropogenic uncertainty, associated to climate scenarios, increased with time and was relevant for Prochlorococcus. The environmental and biological uncertainty, associated to ESMs and niche models, respectively, represented the largest fraction but differed among lineages. Quantifying uncertainties is key because the predicted differences in the future distribution and abundance can have large‐scale consequences on ocean ecosystem functioning.